1. Field of the Invention
This invention relates to a flat panel display device, and more particularly to a flat panel display device and a driving method thereof, wherein input video data are modulated to realize accurate color with a single gamma voltage generator.
2. Discussion of the Related Art
Recently, various flat panel display devices have been developed with reduced weight and size that are capable of eliminating the disadvantages associated with a cathode ray tube (CRT). Such flat panel display devices include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP) and electro-luminescence (EL) panels.
The EL display in such display devices is a self-emission device in which a phosphorous material is excited using recombination of electrons and holes. The EL display device is generally classified into inorganic EL devices and organic EL devices, depending upon a source material for the light-emitting layer. The EL display device has drawn considerable attention due to its advantages such as low voltage driving, self-luminescence, thin-thickness, wide viewing angle, fast response speed, and high contrast ratio.
FIG. 1 is a cross-sectional view showing a related art organic EL structure for explaining a light-emitting principle of the EL display device.
Referring to FIG. 1, the organic EL device includes an electron injection layer 4, an electron carrier layer 6, a light-emitting layer 8, a hole carrier layer 10 and a hole injection layer 12 that are sequentially disposed between a cathode 2 and an anode 14.
If a voltage is applied between a transparent electrode, that is, the anode 14 and a metal electrode, that is, the cathode 2, then electrons produced from the cathode 2 are moved, via the electron injection layer 4 and the electron carrier layer 6, into the light-emitting layer 8, while holes produced from the anode 14 are moved, via the hole injection layer 12 and the hole carrier layer 10, into the light-emitting layer 10. Thus, the electrons and the holes fed from the electron carrier layer 6 and the hole carrier layer 10, respectively, collide at the light-emitting layer 8 to be recombined to generate a light. This light is emitted, via the transparent electrode (i.e., the anode 14), into the exterior to thereby display a picture. Since brightness of the organic EL device is in proportion to supply currents instead of the voltage loaded on each end of the device, the anode 14 is generally connected to a positive current source.
As shown in FIG. 2, an active matrix type EL display device employing such an organic EL device includes an EL panel 16 having pixels 28 arranged at the intersections between gate lines GL and data lines DL, a gate driver 18 for driving the gate lines GL of the EL panel 16, a data driver 20 for driving the data lines DL of the EL panel 16. The active matrix type EL display device further includes a timing controller 40 for controlling driving timing of the data driver 20 and the gate driver 18 and for applying a digital data signal RGB to the data driver 20. The timing controller 40 applies the digital data signal RGB from the exterior (i.e., system) to the data driver 20, and generates a gate control signal GCS, which is required for driving the gate driver 18, and a data control signal DCS, which is required for driving the data driver 20, using vertical/horizontal synchronizing signals and a main clock from the exterior.
The gate driver 18 sequentially applies a scanning pulse to gate lines GL1 to GLn under control of the timing controller 40. The data driver 20 converts a digital data signal inputted from the timing controller 40 into an analog video signal in response to the data control signal (DCS) from the timing controller 40. Further, the data driver 20 applies the analog video signal synchronized with the scanning pulse to data lines DL1 to DLm for each one line.
Each of the pixels 28 receives a data signal from the data line DL when the scanning pulse is applied to the gate line GL, thereby generating a light corresponding to the data signal. To this end, as shown in FIG. 3, each pixel 28 includes an EL cell OEL having a cathode connected to the ground voltage source GND, and a cell driver 30 connected to the gate line GL, the data line DL and the supply voltage source VDD and to the anode of the EL cell OEL to thereby drive the EL cell OEL.
The cell driver 30 includes a switching thin film transistor T1 having a gate terminal connected to the gate line GL, a source terminal connected to the data line DL and a drain terminal connected to a first node N1, a driving thin film transistor T2 having a gate terminal connected to the first node N1, a source terminal connected to the supply voltage source VDD and a drain terminal connected to the EL cell OEL, and a capacitor C connected between the supply voltage source VDD and the first node N1.
The switching thin film transistor T1 is turned on when a scanning pulse is applied to the gate line GL, to thereby apply a data signal supplied to the data line DL to the first node N1. The data signal supplied to the first node N1 is charged into the capacitor C and applied to the gate terminal of the driving thin film transistor T2. The driving thin film transistor T2 controls a current amount I fed from the supply voltage source into the EL cell OEL in response to the data signal applied to the gate terminal thereof, to thereby control an amount of light emitted from the EL cell OEL. Furthermore, since the data signal is discharged from the capacitor C even though the switching thin film transistor T1 is turned off, the driving thin film transistor T2 applies a current I from the supply voltage source VDD until a data signal at the next frame is supplied, to thereby maintain the emission of the EL cell OEL.
The related art EL display device applies a current signal proportional to an input data to each of the EL cells OEL to radiate the EL cells OEL, thereby displaying a picture. Herein, the EL cells OEL includes a R cell OEL having a red (R) phosphorous material, a G cell OEL having a green (G) phosphorous material, and a B cell OEL having a blue (B) phosphorous material in order to implement color. The three R, G and B cells OEL are combined to implement a color for one pixel. Herein, each of the R, G and B phosphorous materials has different light-emission efficiency. In other words, if data signals having the same level are applied to the R, G and B cells OEL, then brightness levels of the R, G and B cells OEL become different from each other. Thus, gamma voltages for each R, G and B cell are set to be different from each other in order to compensate different brightness of R, G and B cells at a same voltage level for the sake of white balance of the R, G and B cells. Accordingly, as shown in FIG. 4, the R, G and B cells include an R gamma voltage generator 32, a G gamma voltage generator 34 and a B gamma voltage generator 36 for generating gamma voltages having different voltage levels, respectively.
As shown in FIG. 5, the R gamma voltage generator 32 generates n gamma voltages (wherein n is an integer) in such a manner to correspond to different brightness data. To this end, the R gamma voltage generator 32 includes (n+1) resistors R11, R12, R13, R14, . . . , R1n+1 connected, in series, between a first supply voltage source VDD1 and a ground voltage source GND. Such an R gamma voltage generator 32 outputs n red gamma voltages RGMA1 to RGMAn corresponding to the bit number of a red digital data signal Rdata inputted from the timing controller 40 to the data driver 20 from nodes between the resistors R11, R12, R13, R14, . . . , R1n+1 connected, in series, between the first supply voltage source VDD1 and the ground voltage source GND.
The G gamma voltage generator 34 generates n gamma voltages in such a manner to correspond to different brightness data as shown in FIG. 5. To this end, the G gamma voltage generator 34 includes (n+1) resistors R21, R22, R23, R24, . . . , R2n+1 connected, in series, between a second supply voltage source VDD2 and a ground voltage source GND. Such an G gamma voltage generator 34 outputs n green gamma voltages GGMA1 to GGMAn corresponding to the bit number of a green digital data signal Gdata inputted from the timing controller 40 to the data driver 20 from nodes between the resistors R21, R22, R23, R24, . . . , R2n+1 connected, in series, between the second supply voltage source VDD2 and the ground voltage source GND.
The B gamma voltage generator 36 generates n gamma voltages in such a manner to correspond to different brightness data as shown in FIG. 5. To this end, the B gamma voltage generator 36 includes (n+1) resistors R31, R32, R33, R34, . . . , R3n+1 connected, in series, between a third supply voltage source VDD3 and a ground voltage source GND. Such an B gamma voltage generator 36 outputs n blue gamma voltages BGMA1 to BGMAn corresponding to the bit number of a blue digital data signal Bdata inputted from the timing controller 40 to the data driver 20 from nodes between the resistors R31, R32, R33, R34, . . . , R3n+1 connected, in series, between the third supply voltage source VDD3 and the ground voltage source GND.
In such first to third supply voltage source VDD1, VDD2 and VDD3, the first supply voltage source VDD1 generates a higher voltage value than the second and third supply voltage sources VDD2 and VDD3 because the R,G and B phosphorous materials have different light-emission efficiencies. In this case, the third supply voltage source VDD3 generates a smaller voltage value than the second supply voltage source VDD2.
Accordingly, the data driver 20 generates analog video signals using the gamma voltages RGMA1 to RGMAn; GGMA1 to GGMAn and BGMA1 to BGMAn corresponding to input digital data signals, of a plurality of gamma voltages RGMA1 to RGMAn; GGMA1 to GGMAn and BGMA1 to BGMAn supplied from the R gamma voltage generator 32, the G gamma voltage generator 34 and the B gamma voltage generator 36, respectively, and applies the generated analog video signals to the data lines DL in such a manner to be synchronized with the scanning signal, thereby displaying a desired picture at the EL panel 20.
However, the related art EL display device has a problem in that, since the data driver 20 includes the R gamma voltage generator 32, the G gamma voltage generator 34 and the B gamma voltage generator 36 for white balance of the R, G and B phosphorous materials having different light-emission efficiencies, its size is enlarged and its cost is increased.